**2.1 Grape and juice composition**

The grape is made up of a large amount of nutrients which will pass into the must once it is crushed which will be able to participate in the formation of the LST of wine. The major components of the grape are sugars, mainly glucose and fructose, which will be transformed into alcohol during fermentation. Nitrogen is an abundant component in grape juice with content around 200–300 mg/L. It appears in two differentiated chemical forms: inorganic (basically as ammonium form) and organic (made up of amino acids, peptides and proteins). The nature and concentrations of amino acids in grapes depend on a wide range of factors, such as fertilization, climatic conditions, and grape variety [8, 9]. They are consumed by yeasts during alcoholic fermentation and can produce some positive volatile compounds, such as esters, or negative ones, such as sulfur volatile compounds, which will influence the final aroma of the wine [10]. Amino acids represent up to 40% of the total nitrogen in wines, and yeasts release some amino acids at the end of fermentation. They act as aromatic precursors through different chemical reactions and to form aromatic compounds. On the other hand, among the minority compounds in wine related to LST, riboflavin should be highlighted. This components is found at very low concentrations (between 3 to 60 μg/L) in grape must [11]. The formation of this compound is related to the *Saccharomyces* metabolism that will play a very important role in the formation of reduction aromas of wine. Finally, sulfur aromatic compounds occur more frequently in wines from vineyards

#### *The Light Struck Taste of Wines DOI: http://dx.doi.org/10.5772/intechopen.99279*

planted in alkaline soils. This is because high pH of soil makes difficult to absorb copper which, normally used as fungicide treatment, helps to eliminate the sulfur compounds produced during winemaking. However, the current trend to replace this metal in new fungicide formulations could lead to an increase in the content of sulfur compounds in wines and therefore the risk of LST appearance. Moreover, the use of sulfur-rich phytosanitary products used in the vineyard may lead to obtaining musts with certain risk of producing this defect.
